score:2
Children do need some documentation in any case. In the past, children could also be included in their parents' passports but I think this is being phased out.
In fact, the requirements are often even more stringent for a child than for an adult because if the child does not appear to be yours (distinct surname), merely having a passport or ID card might not be enough. Similarly, in some countries, children leaving with only one of their parents might need an authorization from the other one.